Drug activity is evaluated against blood and tissue stages of malaria in various animal models including Plasmodium berghei and P. vinckei in mice, P. knowlesi and P. cynomolgi in rhesus monkeys and P. falciparum in owl monkeys. Strains of experimental malarias resistant to various antimalarial drugs and antibiotics are developed and used in studies on mechanisms of drug action, mechanisms of acquired drug resistance, cross resistance to new and old antimalarial compounds and the biology of host-parasite relationships.